Systems and methods for efficient provision of arc welding power source

ABSTRACT

An example welding or cutting circuit includes: an input leg comprising a capacitor coupled between a high bus and a low bus; a buck converter coupled in parallel with the input leg, wherein the buck converter comprises a first transistor, a first diode, and an output electrically coupled to a node between the first transistor and the first diode, and wherein the buck converter is configured to convert input voltage to current in an inductor coupled to the output of the buck converter; and a steering leg coupled in parallel with the input leg, wherein the steering leg is configured to control a rate at which the current in the inductor decreases, and wherein a current detector is positioned at the output to monitor the current, the current detector providing current level indications to a hysteretic controller, the hysteretic controller providing signals to the first transistor that control the transistor to an on state or an off state to control the voltage applied to the inductor.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is continuation of U.S. patent application Ser. No.15/386,674, filed Dec. 21, 2016, entitled “Systems and Methods forEfficient Provision of Arc Welding Power Source,” and claims priority toU.S. Provisional Patent Application Ser. No. 62/271,811, entitled“Systems and Methods for Efficient Provision of Arc Welding PowerSource”, filed Dec. 28, 2015. The entireties of U.S. patent applicationSer. No. 15/386,674 and U.S. Provisional Patent Application Ser. No.62/271,811 are incorporated herein by reference.

BACKGROUND

The present disclosure relates generally to welding power supplies, andmore particularly, to systems and methods for controlling current flowthrough an output load of a power control circuit.

Welding power supply circuits typically convert power from a primarysource to an output suitable for welding operations. The output power isprovided at an appropriate voltage or current level and may becontrolled and regulated according to the process requirements. Somewelding processes require the output to be AC. For instance, typicalhigh current AC outputs for gas tungsten arc welding (GTAW) or submergedarc welding (SAW) may require circuitry that efficiently generates asquare wave output with a magnitude of several hundreds of amperes.Typical circuit topologies designed to meet this need include a buckconverter that steps down a supplied DC voltage, a full bridge inverterthat converts the stepped down DC voltage to an AC output, and an outputclamp circuit that suppresses output energy caused by parasitic outputinductance from welding cables during output current reversal.

Since welding operations generally require high current levels and lowvoltage levels at the output, an important design criterion of typicalwelding and plasma cutting power supply circuits is the limitation ofpower losses in the circuit. However, it is now recognized thattraditional power supply circuits include a combination of components(e.g., buck converter, full bridge inverter, and output clamp circuit)that typically contain multiple transistors and diodes, which greatlycontribute to power losses in the circuit, leading to inefficiencies inthe circuit design. Indeed, it is now recognized that there exists aneed for circuits that reduce the power losses in the circuit andincrease the efficiency of the welding power supply.

BRIEF DESCRIPTION

In an embodiment, a welding or cutting circuit includes an input legincluding a capacitor coupled between a high bus and a low bus.Additionally, the welding or cutting circuit includes a buck convertercoupled in parallel with the input leg. The buck converter includes afirst transistor, a first diode, and an output electrically coupled to anode between the first transistor and the first diode, and the buckconverter converts input voltage to current in an inductor coupled tothe output of the buck converter. Further, the welding or cuttingcircuit includes a steering leg coupled in parallel with the input leg.The steering leg controls a rate at which the current in the inductordecreases.

In an embodiment, a method of controlling current flow through an outputload of a welding or cutting circuit includes pulse width modulatingvoltage from a voltage input leg of a welding or cutting system byswitching a first transistor to provide a level of current through aninductor and an output of the welding or cutting circuit. The firsttransistor is arranged in series with a first diode in a buck converterformation, and the inductor extends from a node between the firsttransistor and the first diode to the output load of the welding orcutting circuit. Additionally, the method includes controlling a currentflow through the inductor and the output of the welding or cuttingcircuit at least in part by switching a second transistor of the weldingor cutting circuit between an open configuration and a closedconfiguration.

In an embodiment, a welding or cutting circuit includes an input leg.The input leg includes a capacitor coupled between a high bus and a lowbus. Additionally, the welding or cutting circuit includes a buckconverter coupled in parallel with the input leg. The buck converterincludes a first transistor, a second transistor, and an outputelectrically coupled to a node between the first transistor and thesecond transistor, and the buck converter converts input voltage tocurrent in an inductor coupled to the output of the buck converter.Further, the welding or cutting circuit includes a steering leg coupledin parallel with the input leg, and the steering leg hystericallycontrols a rate at which the current in the inductor decreases.

DRAWINGS

These and other features, aspects, and advantages of the presentdisclosure will become better understood when the following detaileddescription is read with reference to the accompanying drawings,wherein:

FIG. 1 illustrates an exemplary welding, cutting or heating power supplyin accordance with aspects of the present disclosure;

FIG. 2 is a circuit diagram illustrating an exemplary embodiment of theoutput power control circuit of the welding power supply in accordancewith aspects of the present disclosure;

FIG. 3 is a circuit diagram illustrating an exemplary embodiment of theoutput power control circuit with current flow established from left toright through the output load in accordance with aspects of the presentdisclosure;

FIG. 4 is a circuit diagram illustrating an exemplary embodiment of theoutput power control circuit with current flow freewheeling from left toright through the output load in accordance with aspects of the presentdisclosure;

FIG. 5 is a circuit diagram illustrating an exemplary embodiment of theoutput power control circuit with current flow established from right toleft through the output load in accordance with aspects of the presentdisclosure;

FIG. 6 is a circuit diagram illustrating an exemplary embodiment of theoutput power control circuit with current flow freewheeling from rightto left through the output load in accordance with aspects of thepresent disclosure;

FIG. 7 is a circuit diagram of an exemplary embodiment of the outputpower control circuit illustrating the first step of current reversalfrom left to right to right to left through the output load inaccordance with aspects of the present disclosure;

FIG. 8 is a circuit diagram of an exemplary embodiment of the outputpower control circuit illustrating the second step of current reversalfrom left to right to right to left through the output load inaccordance with aspects of the present disclosure;

FIG. 9 is a circuit diagram of an exemplary embodiment of the outputpower control circuit illustrating the first step of current reversalfrom right to left to left to right through the output load inaccordance with aspects of the present disclosure;

FIG. 10 is a circuit diagram of an exemplary embodiment of the outputpower control circuit illustrating the second step of current reversalfrom right to left to left to right through the output load inaccordance with aspects of the present disclosure;

FIGS. 11A and 11B are graphical representations of exemplary waveformsgenerated during output power control circuit operation;

FIG. 12 is a circuit diagram illustrating an exemplary embodiment of theoutput power control circuit of the welding power supply in accordancewith aspects of the present disclosure;

FIG. 13 is a circuit diagram illustrating an additional embodiment of anoutput control circuit of the welding power supply in accordance withaspects of the present disclosure;

FIG. 14 is a circuit diagram illustrating an embodiment of the outputcontrol circuit of FIG. 13 with current flow freewheeling in a low sideof the output power control circuit from left to right through theoutput load in accordance with aspects of the present disclosure;

FIG. 15 is a circuit diagram illustrating an embodiment of the outputcontrol circuit of FIG. 13 with current flow freewheeling in a high sideof the output power control circuit from left to right through theoutput load in accordance with aspects of the present disclosure;

FIG. 16 is a circuit diagram illustrating an embodiment of the outputcontrol circuit of FIG. 13 with a high side transistor and a low sidetransistor in an open position in accordance with aspects of the presentdisclosure;

FIG. 17 is a circuit diagram illustrating an embodiment of an outputcontrol circuit with four-quadrant hysteretic control in accordance withaspects of the present disclosure;

FIG. 18 is a graph of current through an inductor of the output powercontrol circuit measured by a sensor in accordance with aspects of thepresent disclosure;

FIG. 19 is a circuit diagram illustrating an embodiment of the outputcontrol circuit of FIG. 17 with current flowing through the output loadfrom left to right in accordance with aspects of the present disclosure;and

FIG. 20 is a circuit diagram illustrating an embodiment of the outputcontrol circuit of FIG. 17 with current flowing through an output loadfrom right to left in accordance with aspects of the present disclosure.

DETAILED DESCRIPTION

FIG. 1 illustrates an exemplary welding, cutting or heating power supply10, which functions to power and control a welding, cutting or heatingoperation in accordance with aspects of the present disclosure. Thepower supply unit 10 in the illustrated embodiment contains a controlpanel 12 through which a user may control the supply of materials, suchas power, gas flow, and so forth, to the welding, cutting or heatingoperation through knobs 14 or other panel components. The power supply10 contains ports 16, which may communicatively couple the power supply10 to other system components, such as a torch, a work lead, a wallpower outlet, and so forth. The portability of the unit 10 depends on aset of wheels 18, which enable the user to easily move the power supplyunit 10 to the location of a workpiece.

FIG. 2 is a circuit diagram illustrating one embodiment of an outputpower control circuit 20 of the welding power supply 10 in accordancewith aspects of the present disclosure. The power control circuit 20converts an unregulated DC input to a regulated AC output as needed forthe welding, cutting or heating operation being performed. For instance,typical submerged arc welding (SAW) operations may require a regulatedhigh current square wave output of several hundreds of amperes. However,primary power sources, such as a wall outlet, provide an unregulated ACoutput that is insufficient for a SAW operation. Therefore, it is nowrecognized that circuitry must convert the output of the primary powersource to an output suitable for the welding, cutting or heatingoperation being performed. In operation, the power control circuit 20illustrated in FIG. 2 efficiently converts unregulated DC inputs to afirst capacitor 22 from the primary power supply to regulated AC outputsfor the welding, cutting or heating operation. In the followingdiscussion, the power control circuit 20 illustrated in FIG. 2 may bebroken up into legs and sides for explanatory purposes. However, oneskilled in the art would understand that the components of the circuit20 may be arranged and/or grouped differently while retaining theoverall function of the circuit 20.

A pulse width modulation (PWM) leg 24 modulates current received fromthe first capacitor 22 such that the received unregulated DC current isconverted to a regulated DC current. The PWM leg 24 includes a firsttransistor 26 and a first diode 28 coupled in parallel, a secondtransistor 30 and a second diode 32 coupled in parallel, an inductor 34,and a first terminal 36 of an output 38. The first transistor 26 and thefirst diode 28 may be positioned in between a first node 40 and a secondnode 42. As illustrated in FIG. 2 , the first node 40 may be locatedsuch that it is positioned on a first outer edge 41 of the circuit 20.The second node 42 is located below the first outer edge 41 of thecircuit 20 but above a second outer edge 43 of the circuit 20. Thesecond transistor 30 and the second diode 32 may be positioned inbetween the second node 42 and a third node 44, which may be locatedsuch that it is positioned on the second outer edge 43 of the circuit20. The inductor 34 may be positioned in between the second node 42 andthe first terminal 36 of the output 38 and parallel to the first outeredge 41 and the second outer edge 43 of the circuit 20.

The PWM leg 24 alternates switching of the first transistor 26 or thesecond transistor 30 to increase or decrease current at the output 38 asdictated by the demands of the welding or plasma cutting operation. Insome embodiments, the first transistor 26, the second diode 32, and theinductor 34 may be configured to function as a buck converter.Similarly, in some embodiments, the second transistor 30, the firstdiode 28, and the inductor 34 may be configured to function as a buckconverter, transferring energy from an input to an output by storing andsubsequently releasing energy in the inductor 34. Taken together, thefirst transistor 26, the first diode 28, the second transistor 30, thesecond diode 32, and the inductor 34 may function as a bidirectionalbuck converter, which converts the DC voltage across the first capacitor22 to a regulated DC current in the inductor 34.

A steering leg 46, which includes a third transistor 48 and a thirddiode 50 coupled in parallel and a fourth transistor 52 and a fourthdiode 54 coupled in parallel, forms a half bridge inverter thatdetermines the direction of current flow through the inductor 34. Thesteering leg 46 is positioned between the first outer edge 41 and thesecond outer edge 43 of the circuit 20. During operation, the steeringleg 46 facilitates current flow either from right to left through theinductor 34 or from left to right through the inductor 34 by turning thethird transistor 48 and the fourth transistor 52 on and off. The thirdtransistor 48 and the third diode 50 may be positioned in between thefirst node 40 and a fourth node 56. The fourth transistor 52 and thefourth diode 54 may be positioned in between the fourth node 56 and thethird node 44 such that they exist in series with the first node 40,which is positioned on the first outer edge 41 of the circuit 20, andthe fourth node 56, which is positioned in between the first outer edge41 of the circuit 20 and the second outer edge 43 of the circuit 20. Asecond terminal 58 of the output 38 extending from the fourth node 56 inparallel with the first outer edge 41 and the second outer edge 43 ofthe circuit 20 may be configured to receive current from the steeringleg 46.

An output clamp leg 59 includes a second capacitor 60 that is configuredto function as an output clamp circuit, which suppresses the energy in aparasitic output inductance of the welding or cutting cables duringpolarity reversal. The output clamp leg 59 is positioned between andconnects the first outer edge 41 and the second outer edge 43 of thecircuit 20. In some embodiments, the capacity of the second capacitor 60is much less than the capacity of the first capacitor 22. In someembodiments, the peak current in the second capacitor 60 during polarityreversal may be the current in the inductor 34 and the parasitic outputinductance of the welding or cutting cables.

An input leg 61 includes the first capacitor 22 and a blocking diode 62arranged in series. As illustrated in FIG. 2 , the blocking diode 62 maybe positioned on the first outer edge 41 of the circuit 20 and the firstcapacitor 22 may be positioned in between the first outer edge 41 andthe second outer edge 43 of the circuit 20. The input leg 61 ispositioned between the first outer edge 41 and the second outer edge 43of the circuit 20. The first capacitor 22 is configured to receive powerfrom a primary power source that may include a line frequency step downtransformer and a rectifier. The transformer may be single phase orthree phase and may output 50 Hz or 60 Hz. The transformer may havemultiple primary taps to accommodate multiple input voltages. Theblocking diode 62 allows the second capacitor 60 to resonate with theseries combination of the inductor 34 and the parasitic outputinductance during polarity reversal as described in more detail below.

FIG. 3 is a circuit diagram illustrating an exemplary embodiment of theoutput power control circuit 20 with a current flow 64 established fromleft to right through the inductor 34 (i.e. state 1). To establish theleft to right current flow 64 through the inductor 34, the fourthtransistor 52 is turned on, and the first transistor 26 is pulse widthmodulated to regulate the magnitude of the current through the inductor34. The forward path of current 64 originates from the first capacitor22 and flows through the blocking diode 62, the first node 40, the firsttransistor 26, the inductor 34, the first terminal 36 of the output 38,the output 38, the second terminal 58 of the output 38, the fourth node56, the fourth transistor 52, the third node 44 and back to the firstcapacitor 22. When the pulse width modulation of the first transistor 26dictates that it is off, a freewheel current path 66, as illustrated inFIG. 4 , is established to allow the magnitude of the current flowingthrough the inductor 34 to decrease (i.e. state 2). The freewheelcurrent path 66 flows from left to right through the inductor 34 and isthrough the second diode 32, the second node 42, the inductor 34, thefirst terminal 36 of the output 38, the output 38, the second terminal58 of the output 38, the fourth node 56, the fourth transistor 52, andthe third node 44. The second transistor 30, the first diode 28, thethird diode 50, and the third transistor 48 are not used when DC currentis flowing from left to right through the inductor 34.

FIG. 5 is a circuit diagram illustrating an exemplary embodiment of theoutput power control circuit 20 with a current flow 68 established fromright to left through the inductor 34 (i.e. state 5). To establish theright to left current flow 68 through the inductor 34, the thirdtransistor 48 is turned on, and the second transistor 30 is pulse widthmodulated to regulate the magnitude of the current through the inductor34. The forward path of current 68 originates from the first capacitor22 and flows through the blocking diode 62, the first node 40, the thirdtransistor 48, the second terminal 58 of the output 38, the output 38,the first terminal 36 of the output 38, the inductor 34 the second node42, the second transistor 30, the third node 44 and back to the firstcapacitor 22. When the pulse width modulation of the second transistor30 dictates that it is off, a freewheel current path 70, as illustratedin FIG. 6 , is established to allow the magnitude of the current flowingthrough the inductor 34 to decrease (i.e. state 6). The freewheelcurrent path 70 flows from right to left through the inductor 34 and isthrough the first diode 28, the first node 40, the third transistor 48,the fourth node 56, the second terminal 58 of the output 38, the output38, the first terminal 36 of the output 38, the inductor 34, and thesecond node 42. The first transistor 26, the second diode 32, the thirddiode 50, and the fourth diode 54 are not used when DC current isflowing from right to left through the inductor 34.

In some embodiments, once current flow has been established either inthe left to right current path 64 or in the right to left current path68 through the inductor 34, the direction of the current flow may bereversed. For instance, if current flow has been established in the leftto right current path 64 through the inductor 34, the direction of thecurrent flow can be reversed by turning all the transistors 26, 30, 48,52 off. A first intermediate current flow path 72 illustrated in FIG. 7is established wherein the current continues to flow from left to rightthrough the inductor 34 (i.e. state 3). The first intermediate currentflow path 72 flows from the inductor 34 through the first terminal 36 ofthe output 38, the output 38, the second terminal of the output 58, thefourth node 56, the third diode 50, the first node 40, the secondcapacitor 60, the third node 44, the second diode 30, and the secondnode 42. The inductor 34 releases the energy it stored during the leftto right current flow 64, charging the second capacitor 60 to a voltagegreater than the voltage of the first capacitor 22, at which point theblocking diode 62 begins to block. The second transistor 30 and thethird transistor 48 are turned on to allow the second capacitor tounload its energy back into the output load 38 and the inductor 34 afterthe current in the inductor 34 reaches zero.

When the current in the inductor 34 reaches zero, the voltage on thesecond capacitor 60 is at an upper limit. Subsequently, the energy builtup in the second capacitor 60 will begin to discharge, reversing thedirection of the current flow and establishing a current flow path 74from right to left through the inductor 34, as illustrated in FIG. 8(i.e. state 4). Since the second transistor 30 and the third transistor48 have been turned on, current will flow from the second capacitor 60through the first node 40, the third transistor 48, the fourth node 56,the second terminal of the output 58, the output 38, the first terminalof the output 36, the inductor 34, the second transistor 30, and thethird node 44. When the voltage on the second capacitor 60 discharges tothe voltage on the first capacitor 22, current flow will be establishedthrough the inductor 34 from right to left at approximately the samemagnitude as prior to polarity reversal, slightly reduced by circuitlosses. Subsequently, the third transistor 48 remains on and the secondtransistor 30 is pulse width modulated to regulate the current flowthrough the inductor 34 and reestablish the current path from right toleft as previously shown in FIG. 5 .

Once current flow has been reestablished in the right to left currentpath 68 through the inductor 34, the direction of the current flow canbe reversed by turning all the transistors 26, 30, 48, 52 off. A firstintermediate current flow path 76 illustrated in FIG. 9 is establishedwherein the current continues to flow from right to left through theinductor 34 (i.e. state 7). The first intermediate current flow path 76flows from the inductor 34 through the second node 42, the first diode28, the first node 40, the second capacitor 60, the third node 44, thefourth diode 54, the fourth node 56, the second terminal 58 of theoutput 38, the output 38, and the first terminal of the output 36. Theinductor 34 releases the energy it stored during the right to leftcurrent flow 68, charging the second capacitor 60 to a voltage greaterthan the voltage of the first capacitor 22, at which point the blockingdiode 62 begins to block. The first transistor 26 and the fourthtransistor 52 are turned on to allow the second capacitor to unload itsenergy back into the output load 38 and the inductor 34 after thecurrent in the inductor 34 reaches zero.

When the current in the inductor 34 reaches zero, the voltage on thesecond capacitor 60 is at an upper limit. Subsequently, the energy builtup in the second capacitor 60 will begin to discharge, reversing thedirection of the current flow and establishing a current flow path 78from left to right through the inductor 34, as illustrated in FIG. 10(i.e. state 8). Since the first transistor 26 and the fourth transistor52 have been turned on, current will flow from the second capacitor 60through the first node 40, the first transistor 26, the second node 42,the inductor 34, the first terminal of the output 36, the output 38, thesecond terminal of the output 58, the fourth node 56, the fourthtransistor 52, and the third node 44. When the voltage on the secondcapacitor 60 discharges to the voltage on the first capacitor 22,current flow will be established through the inductor 34 from left toright at approximately the same magnitude as prior to polarity reversal,slightly reduced by circuit losses. Subsequently, the fourth transistor52 remains on and the first transistor 26 is pulse width modulated toregulate the current flow through the inductor 34 and reestablish thecurrent path from left to right as previously shown in FIG. 3 .

FIGS. 11A and 11B illustrate exemplary current and voltage waveformsgenerated during control circuit operation. In particular, FIGS. 11A and11B illustrate an inductor current waveform 80, a second capacitorvoltage waveform 82, a first transistor voltage waveform 84, a secondtransistor voltage waveform 86, a third transistor voltage waveform 88,and a fourth transistor voltage waveform 90. From an initial time 92 toa later time 94, the circuit 20 is switching between state 1 and state 2to maintain the current at the output 38 at 1000 A flowing from left toright through the inductor 34 as previously described with respect toFIGS. 3-4 . The fourth transistor 52 is on in both states 1 and 2 whilethe first transistor 26 is on in state 1 and off in state 2. A currentat the output 38 appears to be a constant 1000 A but is actuallyincreasing a few amps in state 1 and decreasing a few amps in state 2.From a time 94 to a later time 96, the circuit 20 remains exclusively instate 2, the fourth transistor 52 is the only transistor on, and thecurrent at the output 38 is decreasing.

At the time 96, the fourth transistor 52 is turned off, and the circuit20 is in state 3 as previously described with respect to FIG. 7 . Thesecond transistor 30 and the third transistor 48 are turned on in state3 even though the current flow path is through the second diode 32 andthe third diode 50. During state 3, the current at the output 38 rapidlydecreases while the voltage on the second capacitor 60 increases.Subsequently, at a later time 98, the current at the output 38 reverses,and the voltage on the second capacitor 60 is at an upper limit. At thetime 98, the circuit 20 enters state 4, as previously described withrespect to FIG. 8 . The current at the output 38 increases rapidlythrough the second capacitor 60, the second transistor 30, and the thirdtransistor 48. The voltage on the second capacitor 60 begins todecrease.

Subsequently, at an approximate later time 100, the current at theoutput 38 has reversed and is flowing from right to left through theinductor 34. The voltage on the second capacitor 60 has reached itsinitial condition. From the approximate time 100 to an approximate time102, the circuit 20 is in state 5, as previously described with respectto FIG. 5 . The second transistor 30 and the third transistor 48 are on,and the current at the output 38 increases. At the time 102, the currentat the output 38 has reached 1000 A and is flowing from right to leftthrough the inductor 34. The circuit 20 is switching between states 5and 6 to maintain the output current at 1000 A as previously describedwith respect to FIGS. 5-6 . The second transistor 30 is on in state 5while the current at the output is increasing a few amps.

From a time 104 to a later time 106, the circuit 20 is in state 6 aspreviously described with respect to FIG. 6 . The third transistor 48 ison, the second transistor 30 is off, and the current at the output isdecreasing a few amps. At the time 106, the third transistor 48 turnsoff, and the circuit is in state 7 as previously described with respectto FIG. 9 . The first transistor 26 and the fourth transistor 52 turn onin state 7 even though the current flow is through the first diode 28and the fourth diode 54. During state 7, the current at the output 38rapidly decreases, while the voltage on the second capacitor 60increases. At an approximate later time 108, the current at the output38 reverses, and the voltage on the second capacitor 60 is at an upperlimit. At the time 108, the circuit 20 enters state 8 as previouslydescribed with respect to FIG. 10 . The current at the output increasesrapidly through the second capacitor 60, the first transistor 26, andthe fourth transistor 52. The voltage on the second capacitor 60 beginsto decrease.

At an approximate time 110, the current at the output 38 has reversed,and current flow is from left to right through the inductor 34 while thevoltage on the second capacitor 60 has reached its initial condition.From the approximate time 110 to an approximate time 112, the circuit 20returns to state 1, wherein the first transistor 26 and the fourthtransistor 52 are on, and the current at the output 38 increases. At theapproximate time 112, the current at the output 38 has reached 1000 Aflowing from left to right through the inductor 34, and the circuit 20is switching between states 1 and 2 to maintain the output current at1000 A. In the illustrated exemplary operation, the above describedsequence of states repeats for the next 10 mS cycle (i.e. 100 Hzfrequency) of current at the output 38.

FIG. 12 is a circuit diagram illustrating a further embodiment of theoutput power control circuit 20 of FIG. 2 . It is well known to thoseskilled in the art that certain welding processes, such as AC GTAW,require a voltage of approximately 200 volts or more during polarityreversal to maintain current flow and prevent arc rectification. Otherprocess, such as AC SAW, may not require this high voltage duringpolarity reversal, and the embodiment of the output power controlcircuit 20 illustrated in FIG. 12 may be used. In such processes, theoutput clamp leg 59, which includes the second capacitor 60 that isconfigured to function as the output clamp circuit 59 in the embodimentillustrated in FIG. 2 , may be eliminated from the output power controlcircuit 20. Additionally, if the capacitor 60 is eliminated from theoutput clamp circuit 20, then the blocking diode 62, which was part ofthe input leg 61 in FIG. 2 , is no longer required. Accordingly, in theillustrated embodiment, the output current flows through the capacitor22 of the input leg 61 during polarity reversal, and the output voltageis clamped to the voltage on capacitor 22.

FIG. 13 is a circuit diagram illustrating an additional embodiment of anoutput control circuit 120 of the welding power supply 10. Asillustrated, the output control circuit 120 includes a buck converter122 and a steering leg 124. The buck converter 122 includes a transistor126 coupled between the node 40 and the node 42. Additionally, the buckconverter 122 includes a freewheel diode 128 coupled between the node 42and the node 44. Coupled between the first terminal 36 of the output 38and the node 42 is the inductor 34. The steering leg 124 includes afreewheel diode 130 coupled between the node 40 and the node 56 of theoutput control circuit 120, and the steering leg 124 also includes atransistor 132 coupled between the node 56 and the node 44. Further, thesecond terminal 58 of the output 38 is positioned between the freewheeldiode 130 and the transistor 132.

As voltage is applied from the node 40, through the transistor 126 andto the inductor 34, a current at the output 38 may increase beyond acurrent desired for a welding operation. Accordingly, the transistor 126may pulse width modulate or hysterically control the voltage applied tothe inductor 34 to limit the current flowing to the output 38. Tomonitor the current at the output 38, a current detector 134 may bepositioned at the first terminal 36 of the output 38. When controllingthe voltage applied to the inductor 34 using hysteretic control, asillustrated in FIG. 13 , the current detector 134 may provide currentlevel indications to a hysteretic controller 136. Additionally, thehysteretic controller may provide signals to the transistor 126 thatcontrol the transistor 126 to an on state or an off state to control thevoltage applied to the inductor 34.

Further, the hysteretic controller 136 may include a high comparator 138and a low comparator 140. The current level indications from the currentdetector 134 may be supplied to both the high comparator 138 and the lowcomparator 140. Additionally, the high comparator 138 may compare thecurrent level indications to a high reference signal 142, and the lowcomparator 140 may compare the current level indications to a lowreference signal 144. Further, outputs of the comparators 138 and 140are provided to a flip-flop logic gate 146, which ultimately provides acontrol signal to the transistor 126. In this manner, the control signalprovided to the transistor 126 may control the transistor 126 to an offstate (i.e., to decouple the voltage source from the inductor 34) whenthe current level indications are greater than the high reference signal142. Moreover, the control signal provided to the transistor 126 maycontrol the transistor 126 to an on state (i.e., to couple the voltagesource to the inductor 34) when the current level indications are lessthan the low reference signal 144 and/or below the high reference signal142. By coupling the voltage source to the inductor 34, the currentflowing to the output 38 via the inductor 34 increases. Further, bydecoupling the voltage source from the inductor 34, the current flowingto the output 38 via the inductor 34 decreases.

In addition to current control by way of the buck converter 122, thesteering leg 124 may also influence current control at the inductor 34.For example, the transistor 132 may be controlled to on and off statesbased on inputs to a comparator 148 to control a fall time of thecurrent at the inductor 34. It may be appreciated that in someembodiments, the comparator 148 may be a part of the hystereticcontroller 136. For example, when the current is in a path 170, asdescribed in FIG. 16 below, the voltage input from the voltage source isprovided in addition to the voltage of the output 38 to rapidly decreasethe current at the inductor 34. Accordingly, when the current levelindications from the current detector 134 are compared at the comparator148 to a current decrease reference value I_(DECREF) 150, an output ofthe comparator 148 controls whether the current freewheels asillustrated in FIG. 14 , whether the current freewheels as illustratedin FIG. 15 , whether the current flows as illustrated in FIG. 16 , orwhether the current flows along path 152 as illustrated in FIG. 13 .

By way of example, if the current decrease reference value I_(DECREF)150 is set to a relatively high value, the output of the comparator 148may provide a signal to the transistor 132 such that the transistor 132remains closed under all situations where the current level indicationsfrom the current detector 134 remain below I_(DECREF) 150. On the otherhand, when I_(DECREF) 150 is set relatively low, or the current levelindications from the current detector 134 exceed the current levelindications, the comparator 148 may output a low signal that results inthe transistor 132 opening. In this situation, the current at theinductor 34 may rapidly decrease due to the combination of the inputvoltage from an input bus 154 and the voltage of the output 38 appliedto the inductor 34. In general, I_(DECREF) 150 may be set to a levelsufficiently greater than the high reference signal 142. In this manner,the transistor 132 may not be opened when efficient control of thecurrent across the inductor 34 is accomplished by control of the buckconverter 122.

FIG. 14 is a circuit diagram illustrating the output control circuit 120with a current flow path 158 freewheeling in a low side 158 of theoutput control circuit 120 from left to right through the inductor 34and the output 38. In the illustrated circuit diagram, the transistor132 is closed, which indicates that the current level indications fromthe current detector 134 are less than I_(DECREF) 150. Additionally, thetransistor 126 is open, which indicates that the current levelindications from the current detector 134 are greater than the highreference signal 142. Alternatively, in a PWM embodiment, when thetransistor 126 is open, a PWM signal supplied to the transistor 126 islow. Immediately prior to either of these situations occurring, thecurrent at the output 38 may be greater than an ideal welding current,but not sufficiently high for the steering leg 124 to assist incontrolling the current to a lower level at a faster rate, as discussedabove.

Additionally, because the current path 158 is freewheeling in the lowside 160 of the output control circuit 120, the current at the output 38may decrease at a rate that is represented by the voltage at the output38 divided by an inductance of the inductor 34. Accordingly, because thevoltage from the input bus 154 is not added to the voltage at the output38, a fall time for the current at the output 38 may be slower than whenboth the transistors 126 and 132 are open, as discussed below inrelation to FIG. 16 . The reduced fall rate associated with the currentpath 158 may be desirable when the current at the output 38 isrelatively close to a desired current for a welding operation. In thismanner, the transistor 126 may control application of the voltage fromthe input bus 154 as the current alternates between falling below thehigh reference signal 142 and increasing above the high reference signal142.

FIG. 15 is a circuit diagram illustrating the output control circuit 120with a current flow path 164 freewheeling in a high side 162 of theoutput control circuit 120 from left to right through the inductor 34and the output 38. In the illustrated circuit diagram, the transistor132 is open, which indicates that the current level indications from thecurrent detector 134 are greater than I_(DECREF) 150. Additionally, thetransistor 126 is closed, which may indicate that the current levelindications from the current detector 134 are less than the highreference signal 142. Accordingly, the current at the output 38 may bein an efficient working range for a welding operation, but I_(DECREF)150 may have been temporarily set to relatively low value, such asduring a power down operation. Therefore, the steering leg 124 is in aconfiguration to assist in controlling the current to a lower level.

Additionally, because the current path 164 is freewheeling in the highside 162 of the output control circuit 120, the current at the output 38may decrease at a rate similar to the rate described above in thediscussion of FIG. 14 . Therefore, controlling either of the transistors126 or 132 hysterically or using PWM may result in a similar currentreduction rate when one of the transistors 126 or 132 is closed whilethe other transistor 126 or 132 is open. In the embodiment illustratedin FIG. 15 , the transistor 132 may remain open until the current at theoutput 38 falls below I_(DECREF) 150 so that the current at the output38 may fall to a desired level. Alternatively, using PWM control of thetransistor 132, the transistor 132 may remain open until the PWM controlprovides a high signal to the transistor 132.

FIG. 16 is a circuit diagram illustrating the output control circuit 120of FIG. 13 with the transistors 126 and 132 in an open position. Withthe transistors 126 and 132 in the open position, the freewheel diodes128 and 130 pass a current flow path 170 from the inductor 34, throughthe output 38, and back to the capacitor 22. In this manner, a highvoltage is provided across the inductor 34. Because di/dt=V/L, andbecause the high voltage is provided across the inductor 34, the rate ofcurrent fall (i.e., di/dt) is much greater than the rate of current fallin FIG. 14 or FIG. 15 .

Because the transistor 126 is in an open position, using the hystereticcontroller 136 of FIG. 13 , the current level indications from thecurrent detector 134 are greater than the high reference signal 142 forthe hysteretic controller 136 to provide the signal to open thetransistor 126. Additionally, because the transistor 132 is also open,the current level indications from the current detector 134 are alsogreater than the I_(DECREF) 150 for the comparator 148 to provide thesignal to open the transistor 126. Accordingly, when the current isgreater than both the high reference signal 142 and I_(DECREF) 150, itmay be desirable to decrease the current flow across the inductor 34 ina manner more rapid than when just a single transistor 126 or 132 is inan open position and the current flow, as discussed above in thediscussion of FIGS. 14 and 15 . Additionally, using PWM control, a lowPWM signal applied to both the transistor 126 and the transistor 132results in both the transistors 126 and 132 in the open position.

Although illustrated in FIGS. 14-16 as including the transistor 126 andthe diode 128 positioned in the buck converter 122 such that thetransistor 126 is coupled to the high bus (i.e., V_(bus) ⁺) of theoutput control circuit 120 and the diode 128 is coupled to the low bus(i.e., V_(bus) ⁻) of the output control circuit 120, and including thediode 130 and the transistor 132 positioned in the steering leg 124 suchthat the diode 130 is coupled to the high bus (i.e., V_(bus) ⁺) of theoutput control circuit 120 and the transistor 132 is coupled to the lowbus (i.e., V_(bus) ⁻) of the output control circuit 120, in otherembodiments, the position of the transistor 126 and the diode 128 of thebuck converter 122 may be swapped, and the position of the diode 130 andthe transistor 132 of the steering leg 124 may be swapped. In otherwords, in certain embodiments, the diode 128 of the buck converter 122may be coupled to the high bus (i.e., V_(bus) ⁺) of the output controlcircuit 120 and the node 42 connecting the output 38 of the outputcontrol circuit 120 while the transistor 126 of the buck converter 122may be coupled to the low bus (i.e., V_(bus) ⁻) of the output controlcircuit 120 and the node 42 connecting the output 38 of the outputcontrol circuit 120, and the transistor 132 of the steering leg 124 maybe coupled to the high bus (i.e., V_(bus) ⁺) of the output controlcircuit 120 and the node 56 connecting the output 38 of the outputcontrol circuit 120 while the diode 130 of the steering leg 124 may becoupled to the low bus (i.e., V_(bus) ⁻) of the output control circuit120 and the node 56 connecting the output 38 of the output controlcircuit 120. Control of such an embodiment of the output control circuit120 will be substantially similar to that discussed above with respectto FIGS. 14-16 .

FIG. 17 is a circuit diagram illustrating an embodiment of an outputcontrol circuit 178 with four-quadrant hysteretic control. The outputcontrol circuit 178 includes the transistors 126 and 132, which are alsopresent in the output control circuit 120 of FIGS. 13-16 . Additionally,the freewheel diodes 128 and 130 are replaced by transistors 180 and 182to provide four-quadrant control of the output control circuit 178. Thehysteretic controller 136 and the comparator 148 may perform asdescribed above in the discussion of FIG. 13 . However, in addition tocontrolling the transistors 126 and 132, respectively, the hystereticcontroller 136 and the comparator 148 may also provide control signalsto the transistors 180 and 182, respectively. In general, thetransistors 180 and 182 may be opened when the transistors 126 and 132are closed, and the transistors 180 and 182 may be closed when thetransistors 126 and 132 are opened. To accomplish this logic control, aninverter 184 may couple between the transistor 180 and the hystereticcontroller 136, and an inverter 186 may couple between the transistor182 and an output of the comparator 148. In this manner, control signalsthat are opposite of the control signals provided to the transistors 126and 132 are provided to the transistors 180 and 182.

In the illustrated embodiment, the path 152 represents the flow ofcurrent from the input leg 61 and through the output load 38. Asillustrated, the path 152 runs left to right through the output load 38and from a positive bus 154 to a negative bus 156. Accordingly, thecontrol of the transistors 126, 132, 180, and 182 provides a similarcurrent path to that of FIGS. 3 and 13 .

It may be appreciated that while the transistors 180 and 182 arecontrolled based on control signals received by the transistors 126 and132, respectively, in some embodiments, each of the transistors 126,132, 180, and 182 may have individual hysteretic control circuitry. Thatis, a hysteretic controller 136 may be provided for each of thetransistors 126, 132, 180, and 182, and each of the hystereticcontrollers 136 may be controlled independently of each other based.Additionally, in another embodiment, the hysteretic controller 136 maycontrol the transistors 126 and 180, as illustrated in FIG. 17 , whileeach of the transistors 132 and 182 have individual comparators 148 forcontrolling the transistors 132 and 182 independent of each other.Moreover, any combination of the hysteretic controllers 136 and thecomparators 148 provided to control the transistors 126, 132, 180, and182 is also conceived.

Further, while FIG. 17 depicts inverters 184 and 186, it may beappreciated that a switching mechanism may also be used to provide thecontrol signals to the transistors 126, 132, 180, and 186. For example,instead of using the inverter 184, a switching device may switch a highcontrol signal between the transistor 126 and the transistor 180 basedon input received from the hysteretic controller 136. In such anembodiment, the transistors 126 and 180 are opened when the high signalis switched away from the gate input of the transistors 126 and 180.This switching may be controlled by the hysteretic controller 136.Similarly, another switching device may be used in place of the inverter186 and controlled by the comparator 148. While the circuit diagrams ofFIGS. 13-17 include the inductor 34 electrically coupled between thebuck converter 122 and the output 38, in other embodiments, the inductor34 may be electrically coupled between the output 38 and the steeringleg 124 (e.g., to node 56).

FIG. 18 is a graph of current 181 through the inductor 34 measured bythe sensor 134 as received by the hysteretic controller 136. Thehysteretic controller 136 may output the high reference signal 142, thelow reference signal 144, and the I_(DECREF) signal 150 to control thecurrent through the inductor 34 based on the measured current 181. Attime t1, the comparators 138 and 140 of the hysteretic controller 136may control the flow of current 181 through the inductor 34. Forexample, when the current 181 exceeds the high reference signal 142 attime t2, the transistor 126 may be transitioned to an off state to causethe current 181 through the inductor 34 to decrease. At time t3, whencurrent decreases below the low reference signal 144, the transistor 126may be transitioned to an on state to cause the current 181 to throughthe inductor 34 to increase. In this manner, the hysteretic controller136 may approximate a command signal 183. In some embodiments, the highreference signal 142 and the low reference signal 144 may be a presetdifference from the command signal 181.

During times t4-t7, the hysteretic controller 136 may control thesteering leg 124 (e.g., transistors 132 and 182 in the embodimentillustrated in FIG. 17 ) during a decrease in current 181 through theinductor 34. The current 181 may decrease due to any suitable reason,such as during termination of the weld, during a phase of pulsedwelding, input from an operator, or the like. At time t4, the current183 begins to decrease due to control, for example, of the transistors126 and 180. That is, the hysteretic controller 136 may continue tocontrol the current 136 based on the decreasing high reference signal142 and the low reference signal 144 by opening and closing thetransistors 126 and 180. For example, the hysteretic controller 136 maycause the transistor 126 to be in an off state when the current 183exceeds the high reference 142.

In some embodiments, the current 181 through the inductor 34 may notdecrease at a rate fast enough due to operation of the buck converter122 alone. To control the rate at which current in the inductor 34decreases, the comparator 148 of the hysteretic controller 136 mayoutput a signal to control the state of the transistor 132 based on thedecreasing I_(DECREF) signal 150 in addition to, for example, thetransistors 126 and 180 of the buck converter 122. That is, at time t5,the current 181 may exceed the high reference signal while thetransistor 126 is open and the transistor 180 is closed. To furtherdecrease the current 181 through the inductor 34 at a faster rate thanfrom control of the transistors 126 and 180, the comparator 148 of thehysteretic controller 136 may send a control signal to transistor 132 totransition the transistor 132 to an off state when the current 181exceeds the I_(DECREF) signal. Switching the transistor 132 to the offstate causes the current 181 to decrease at a faster rate than if thetransistor 132 is in the on state. In some embodiments, the current 181may not decrease fast enough to fall between the high and low limits orfall below the I_(DECREF) signal while the transistor 132 is in the offstate. As such, in some embodiments, the transistor 132 may maintain anoff state throughout the decrease in current 181 to enable current 181to decrease at a faster rate than if the transistor 132 were in an onstate. In the illustrated embodiment, if the current decreases at afaster rate than the I_(DECREF) signal, then the transistor 132 may beswitched to an on state to control the decrease in current 181. Forexample, at time t6, the transistors 126 and 132 may be transitioned toan on state when the current 181 decreases below the I_(DECREF) signal.As shown in the illustrated embodiment, there may be some hysteresis inthe circuit that alters the reference value when the switch changesstates. The process may be repeated at t7 in which the current againexceeds the I_(DECREF) signal 150.

FIG. 19 is a circuit diagram of the output control circuit 178 when thehysteretic controller 136 provides a signal that opens the transistor126 and closes the transistor 180. Additionally, a comparator controller188, which includes the comparator 148, provides a signal that opens thetransistor 132 and closes the transistor 182. The result of such acontrol scheme is the path 170 of the current flow that is similar tothe path 170 of the current flow illustrated in FIG. 16 . Asillustrated, the path 170 flows from the negative bus 156 to thepositive bus 154, and the path 170 flows from left to right across theoutput load 38.

With the transistors 126 and 132 in the open position, the transistors180 and 182 in a closed state provide a current flow path 170 from theinductor 34, through the output 38, and back to the capacitor 22. Inthis manner, a high voltage is provided across the inductor 34. Becausedi/dt=V/L, and because the high voltage is provided across the inductor34, the rate of current fall (i.e., di/dt) is much greater than the rateof current fall in FIG. 14 or FIG. 15 , for example. Additionally, asstored energy in the inductor 34 is discharged, stored energy in thecapacitor 22 increases until the current across the output 38 reverses.

Accordingly, FIG. 20 is a circuit diagram of the output control circuit178 when the hysteretic controller 136 provides a signal that opens thetransistor 126 and closes the transistor 180, and the current flowingacross the output 38 reverses after rapidly decreasing in FIG. 18 . Theresult of a reversal in the current flow path 170 is a path 190 of thecurrent flow. As illustrated, the path 190 flows from the positive bus154 to the negative bus 156, and the path 190 flows from right to leftacross the output load 38.

In reversing the flow of current across the output load 38, the currentlevel across the inductor 34 may increase in a negative direction untilthe hysteretic controller 136 and/or the comparator controller 188control the current level to a steady state and/or back toward a zerocurrent state. As the current across the inductor 34 increases, theenergy stored in the capacitor 22 may decrease. Additionally,controlling the current level to a steady state or toward zero may occurin a manner similar to the control for the current path 152 described inrelation to FIGS. 13 and 17 . Further, the output control circuit 178may generally cycle back and forth between a positive current across theinductor 34 and a negative current across the inductor 34 using themethods described above.

While only certain features of the present disclosure have beenillustrated and described herein, many modifications and changes willoccur to those skilled in the art. It is, therefore, to be understoodthat the appended claims are intended to cover all such modificationsand changes as fall within the true spirit of the present disclosure.

What is claimed is:
 1. A welding or cutting circuit, comprising: an input leg comprising a capacitor coupled between a high bus and a low bus; a buck converter coupled in parallel with the input leg, wherein the buck converter comprises a first transistor, a first diode, and an output electrically coupled to a node between the first transistor and the first diode, and wherein the buck converter is configured to convert input voltage to current in an inductor coupled to the output of the buck converter; and a steering leg coupled in parallel with the input leg, wherein the steering leg is configured to control a rate at which the current in the inductor decreases, and wherein a current detector is positioned at the output to monitor the current, the current detector providing current level indications to a hysteretic controller, the hysteretic controller providing signals to the first transistor that control the transistor to an on state or an off state to control the voltage applied to the inductor.
 2. The welding or cutting circuit of claim 1, wherein steering leg is configured to control the rate at which the current in the inductor decreases by controlling a path through which the current flows in the welding or cutting circuit.
 3. The welding or cutting circuit of claim 1 or 2, wherein the steering leg comprises a second transistor and a second diode, wherein a node between the second transistor and the second diode is configured to couple to an output load.
 4. The welding or cutting circuit of claim 3, wherein the first transistor and the second diode are each coupled to the high bus, and the first diode and the second transistor are each coupled to the low bus, or wherein the first transistor and the second diode are each coupled to the low bus, and the first diode and the second transistor are each coupled to the high bus.
 5. The welding or cutting circuit of claim 3, wherein the first transistor is configured to open when the current in the inductor is greater than a current threshold value, or wherein the second transistor is configured to open when the current in the inductor is greater than a current threshold value.
 6. The welding or cutting circuit of claim 5, wherein the current threshold value is configured to change depending on a mode of output control circuitry.
 7. The welding or cutting circuit of claim 3, wherein the steering leg is configured to reverse a direction of the path through which the current flows across the inductor.
 8. The welding or cutting circuit of claim 3, wherein the steering leg comprises a third transistor and a fourth transistor, wherein a node between the third transistor and the fourth transistor is configured to couple to an output load, wherein the steering leg comprises a current sensor coupled to the output and a comparator that controls the third transistor and the fourth transistor based on a comparison between a measured output current and a current command value.
 9. The welding or cutting circuit of claim 1, wherein the buck converter and the steering leg are hysterically controlled based on a signal provided by the current sensor.
 10. A method comprising: controlling voltage from a voltage input leg of a welding or cutting circuit by switching a first transistor of the welding or cutting circuit between an open configuration and a closed configuration to control a level of current through an inductor and an output of the welding or cutting circuit, wherein the first transistor is arranged in series with a first diode in a buck converter formation of the welding or cutting circuit, and the inductor extends from a node between the first transistor and the first diode to an output load of the welding or cutting circuit; and controlling a current flow through the inductor and the output of the welding or cutting circuit at least in part by switching a second transistor of the welding or cutting circuit between an open configuration and a closed configuration, monitoring the current at the output, providing current level indications to a hysteretic controller, the hysteretic controller providing signals to the first transistor that control the transistor to an on state or an off state to control the voltage applied to the inductor.
 11. The method of claim 10, further comprising increasing a fall rate of an output current by controlling the first transistor and the second transistor to the open configuration.
 12. The method of claim 10, further comprising controlling switching of the first transistor based on at least one comparison between a measured output current and a reference signal.
 13. The method of claim 10, further comprising controlling switching of the second transistor based on at least one comparison between a measured output current and a current command value, wherein the current command value is adjustable during an operation of the welding or cutting circuit.
 14. The method of claim 10, further comprising controlling switching of the first transistor and the second transistor based on at least a measured output current. 